| While I built my dual-carb intake from
stainless steel, I dediced to make my boosted EFI intake out of
aluminum. Aluminum is so much easier to machine and work with, although
much more difficult to weld. It's also so much lighter. Once I had decided upon the basic layout of the intake manifold, I ordered some aluminum 45x3 mm U-bends, a 4" round tube and end caps for it, from AMW Dynoservice. The runners (U-bends) have a 3 mm wall thickness, so the ID is 39 mm (1.54"). Don't be fooled to think they came polished - I spent many hours sanding and polishing them before welding together. It's much easier to polish loose parts. The fuel rail and the injectors come from Sportti-Auto, while Race Performance supplied the 80 mm throttle body. The throttle body is a universal Chinese make. It comes with a flange that you can weld on your own intake plenum. The intake port flanges were waterjet cut from a 10 mm aluminum bar (thanks to my friend Leo Laurell). |
 Rather than build a traditional log-style manifold with the throttle-body at the end of the plenum, my goal was to make the intake manifold as symmetrical as possible, to ensure each cylinder gets equal fill. That's why I decided to mount the throttle body at the center of the plenum. The size of the plenum, in a boosted application, should be at least equal to the size of the engine, or preferably more. The idea, I think, is to minimize the effect of one induction pulse to the next one. The Buick straight-8 likes long runners to keep the air column moving at low speeds, especially due to the high rod-to-stroke ratio. I wanted the runners to be long and equal-length, and this is the outcome of my thinking process. As seen, the injectors are aiming straight at the back of the intake port (only 2 injectors installed here to mock up fuel rail location). At 6000 rpm, the maximum pulse width (at 50% duty cycle) will be 5 milliseconds. With that in mind, and a target of 400+ HP with only 4 injectors, the injectors need to be as big as you can get. Then again, they need to be as linear as you can get. I chose state-of- the-art Injector Dynamics ID 2000. Probably the best and most expensive on earth ! |
 The runner entry inside the plenum should have a conical "bell-mouth" shape to provide undisturbed flow to the runner. In this case, the runners start with machined "flow rings" inside the plenum, also supplied by AMW Dynoservice. They help proving a smooth turn for the airflow entering the runner. It's takes surprisingly lot of work converting an old carbureted car into an EFI. You need to convert to electric fuel pump, build a return line to the tank, and the whole fuel system must tolerate a much higher pressure. You need to eliminate the mechanical linkage from gas pedal to carbs, and fabricate a system that uses a throttle cable. Should I remove and block the mechanical fuel pump? That would eliminate vacuum pump, too, necessitating an electric wiper motor. Should I leave it? Suggestions? |
| To be continued ;-) |
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